Project Summary Ultraviolet B (UVB) radiation has profound effects upon skin and generates systemic consequences from fever to immunosuppression to vitamin D production. As UVB only penetrates the epidermis, a major question in photobiology is how UVB-treated skin sends systemic signals. Recent studies have indicated that small membrane-bound vesicles known as microvesicle particles (MVP) released from cells in response to various stressors can act as potent signaling agents due to their ability to carry nuclear and cytoplasmic components. We have demonstrated that UVB generates MVP release from epithelial cells and skin, which could provide a potential mechanism for UVB-mediated systemic signaling. Our group and others have demonstrated that UVB radiation generate high levels of the lipid mediator Platelet-activating factor (PAF) produced enzymatically and PAF-receptor (PAF-R) agonists produced non-enzymatically via reactive oxygen species. Recent studies using antioxidants and PAF-R-expressing/null cell lines have implicated involvement of PAF-R signaling in UVB generated MVP (UVB-MVP). Two aims are designed to test the hypothesis that UVB generates MVP in human skin in a PAF-dependent manner and transfers systemic effects via their carried potent signaling molecules. Aim 1 will determine if MVP are released from human skin following UVB and if this process is PAF-R dependent. We plan three complementary approaches. First, we will use human skin explants to induce multiple suction blisters with the blister fluid as source of MVP, and test effects of PAF-R antagonists/antioxidants. Second, we will induce suction blisters on human subjects with/without systemic antioxidants, and treat the blister roof with UVB. Finally, we will assess circulating MVP in vivo using paired blood draws (before/after phototherapy) from human patients undergoing whole body UVB treatment. Aim 2 will determine the bioactive agents in UVB-MVP. Both MVP and cells will be tested for three classes of agents: lipid mediators, protein cytokines and microRNAS. Successful completion of this project will (i) address an important question in photobiology as to how a keratinocyte-specific stimulus can generate systemic signaling effects, (ii) offer pharmacologic mechanisms to block UVB systemic effects.